This project is a continuation (DE08450) of efforts to produce a non- shrinking, high performance dental resin system with optimal cure characteristics, structural integrity, and biocompatibility that has the potential of long term clinical success as a stable matrix resin for dental composites. The successful development of such a material would greatly increase the longevity of dental composite/adhesive systems and substantially improve dental patient care. In order to achieve our goal, the following specific aims will be investigated; 1) to synthesize the most promising alicyclic/aromatic spiroorthocarbonates (SOCs) that demonstrate expansion during polymerization and have optima solubility parameters and polymerization rates during curing; 2) to produce epoxy copolymers that are compatible with the SOCs, are non-toxic, and have suitable physical and mechanical properties, including cure rate, for us clinically; 3) to determine the appropriate initiators and sensitizers so that the SOC/epoxy comonomers can be photo cured with visible light and with a high degree of conversion; 4) to perform kinetic experiments which will characterize the rates and extent of copolymerization during the curing reaction of the S0C/epoxy materials; 5) to evaluate the physicochemical, mechanical, and biocompatibility characteristics of the SOC/epoxy resin mat formulations. The main hypothesis to be tested throughout this project is "SOC expanding monomers in combination with suitably formulated epoxy comonomer will produce resins that posses superior properties and clinical performance compared to traditional composite matrix resins because they will be nonshrinking, have a high degree of cure, and be mechanically and hydrolytically stable." The research design and methods include four phases. The first phase involves the development and synthesis of specific SOC monomers having appropriate solubility parameters and cure rates. The second phase is the development of epoxy comonomers containing polyhydroxy additives and using sensitized onium salt chemistry to initiate the reactions. The third phase involves investigating the type and extent of the copolymerization reactions taking place between the epoxy comonomer and the SOC monomer. The fourth phase of the project involves characterizing the physical/mechanical and biocompatibility characteristics of promising copolymer candidates. This phase involves using many standard ASTM and IS0 test methods to characterize such properties as setting time, working time, fracture toughness, fatigue strength, tensile strength, modulus of elasticity, water sorption and solubility, and dimensional change upon curing. Biocompatibility properties of mutagenicity and cytotoxicity will also be determined. By the end of the five year funding period, it is anticipated that a new nonshrinking SOC/epoxy resin matrix material will have been produced, tested, and optimized which will substantially improve the clinical performance of dental composite resins.